CMOS-microprocessor chip and package anti-resonance method

ABSTRACT

A method for regulating resonance in a micro-chip has been developed. The circuit includes an on-chip de-coupled capacitor that is shunted across the supply and ground voltages, and a band-pass shunt regulator that is in parallel to the capacitor across the supply and ground voltages. The regulator will short circuit the supply and ground voltages at a pre-determined frequency to reduce the resonance effect on the micro-chip.

BACKGROUND

As microprocessor circuits have achieved greater and greater speeds, these circuits have become more and more sensitive to the effects of parasitic inductance. The parasitic inductance can come from such sources as bond wires, IC package leads, and external supply lines that provide operating power. The problem with such characteristics is that they form a very high supply line impedance at the resonance frequency. This may lead to circuit oscillation 10 as shown in FIG. 1. In order to avoid such undesirable effects on circuit operation, the inductance must be suitably controlled.

Prior art methods of controlling parasitic inductance include connecting an external capacitor between the supply leads. This connection creates a passive bypass that decreases the supply line oscillation due to external inductances. However, it does not significantly reduce the oscillation caused by internal inductances. Another prior method includes connecting on on-chip capacitor between the internal supply leads. The capacitor acts as a bypass in the same manner as an external capacitor. The resulting non-oscillating circuit performance is shown in FIG. 2. However, in order to be effective, the internal capacitor must be very large. This has the drawback of occupying a significant portion of the chip area. Consequently, this method is generally undesirable when minimization of the die area is of great importance.

Another prior art approach involves increasing the amount of charge stored or delivered to a given amount of added on-chip de-coupling capacitance by actively increasing the voltage variation across their terminals. FIG. 3 shows a schematic of this technique with resistance losses. In this method, fully charged capacitors 32 and 34 of equal value are stacked in series 36 across the on-chip Vdd/Vss grid. The capacitors serve as a voltage multiplier for the Vdd/Vss grid. The depleted voltage in each capacitor is Vdd/n, where n is the number of capacitor stacks. Conversely, the stacked capacitors will store charge from the Vdd/Vss grid until the terminals across the capacitors are fully at Vdd.

A capacitance amplification factor (G) represents the charge supplied to the grid by the switched capacitors normalized to the charge furnished by regular de-coupled capacitors given the same supply voltage variation. The amplification can be expressed as G=(k+n−1)/(k*n²), where n is the number of stacks and k is the voltage regulation tolerance. With each capacitor having a value (Cd), the equivalent unstacked capacitance of Cd*n is reduced to Cd/n upon stacking with a total stack voltage of Vdd*n.

FIG. 4a shows a schematic 40 of an implementation of the method. The circuit shows mutually exclusive CMOS switches the configure the capacitors (C1) 50 and (C2) 52 to either be in the charging phase (shunt across Vdd/Vss) or in the discharging phase (in series with Vdd/Vss). The circuit has two sections: the V_(ave) (average voltage) tracking loop 42 and the V_(inst) (instant voltage) monitor and charge pump loop 44. The switches are driven by two complementary driver 46 and 48. These drivers each provide 2 outputs with enough voltage offset to ensure minimal leakage through both charge and discharge switches during switching activity.

Instantaneous voltage supply variation (V_(inst)) is monitored by coupling the Vdd and Vss onto a comparator 48 input that is dynamically biased about a reference voltage (V_(ave)). V_(ave) is a high-pass filtered version of the local ((Vdd−Vss)/2. Its low frequency cutoff clears the low end resonance range, but it also rejects the tracking of low-frequency disturbances that are not due to resonance. The coupled V_(inst) feed the main negative feedback loop as charge is pumped in and out of the switched capacitors 50 and 52 coupled to the Vdd/Vss grid in an attempt to defeat the voltage variations. The compensated high frequency cutoff ensures stable loop response while also clearing the high end of the resonance range.

FIG. 4b shows the operation 54 of the circuit shown in FIG. 4a. Specifically, the graph shows: a steady state when V_(inst)=V_(ave); a discharging phase when V_(inst)<V_(ave); and a charging phase when V_(inst)<V_(ave). The high frequency and low frequency cutoffs are also shown for their respective phases.

While the method of using stacked capacitors has been demonstrated to be effective in minimizing the effect of parasitic inductance, space is at a premium in microprocessor design. Any method of obtaining the same performance while reducing the required area on the chip yields significant cost benefits.

SUMMARY OF INVENTION

In some aspects the invention relates to a method for regulating resonance in a micro-chip comprising: connecting a de-coupling capacitance across a microchip supply voltage and a micro-chip ground voltage; connecting a band-pass shunt regulator across the micro-chip supply voltage and the micro-chip ground voltage; and short circuiting the micro-chip supply voltage and the micro-chip ground voltage with the band-pass shunt regulator at a pre-determined voltage.

The advantages of the invention include, at least, provide regulation a resonance in a micro-chip with a reduce area requirement that results in reduced die size and decreased cost.

The advantages of the invention include, at least, provide regulation a resonance in a micro-chip with a reduce area requirement that results in reduced die size and decreased cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a graph of an oscillating circuit.

FIG. 2 shows a graph of a non-oscillating circuit.

FIG. 3 shows a schematic of prior art stacked series capacitors.

FIG. 4a shows a schematic of a prior art tracking loop and monitor charge pump loop.

FIG. 4b a graph of the charging and discharging cycle of the circuit shown in FIG. 4a.

FIG. 5 shows a schematic of one embodiment of the present invention.

DETAILED DESCRIPTION

Exemplary embodiments of the invention will be described with reference to the accompanying drawings. Like items in the drawings are shown with the same reference numbers.

FIG. 5 shows a schematic of one embodiment of the present invention. The figure shows a circuit similar to that shown in FIG. 4a. However, the present invention has an added band-pass-shunt regulator 60 in parallel to the circuit. The shunt regulator 60 includes two transistors: a PMOS or “p-type” transistor 62 and a NMOS or “n-type” transistor 64.

The transistors 62 and 64 are in series with each other. The entire shunt regulator 60 is tied across the Vdd and Vss power supply lines. The regulator 60 will short the supply voltage (Vdd) with the ground (Vss) at a certain resonance frequency. This frequency is determined by the characteristics of the components of the regulator. Once the regulator shorts the supply and ground voltages, it in effect acts as a damping resistor and consequently reduces the resonance effect on the circuit. While FIG. 5 shows only one regulator, it is possible to use multiple regulators according to the design criteria of the circuit.

The use of a band-pass shunt regulator will reduce the required chip area for the circuit by over 50% due to the lessened load on the other components. The net result is a reduction in die size and cost without a degradation in performance While the invention has been disclosed with reference to specific examples of embodiments, numerous variations and modifications are possible. Therefore, it is intended that the invention not be limited by the description in the specification, but rather the claims that follow. 

What is claimed is:
 1. A method for regulating resonance in a micro-chip comprising: connecting a de-coupling capacitance across a micro-chip supply voltage and a micro-chip ground voltage; connecting a plurality of band-pass shunt regulators across the micro-chip supply voltage and the micro-chip ground voltage; and short circuiting the micro-chip supply voltage and the micro-chip supply voltage with the band-pass shunt regulators at a pre-determined voltage.
 2. The method of claim 1, further comprising connecting a plurality of de-coupling capacitances across the micro-chip supply voltage and the micro-chip ground voltage.
 3. A method for regulating resonance in a micro-chip comprising: connecting a de-coupling capacitance across a micro-chip supply voltage and a micro-chip ground voltage; connecting a band-pass shunt regulator across the micro-chip supply voltage and the micro-chip ground voltage; and short circuiting the micro-chip supply voltage and the micro-chip supply voltage with the band-pass shunt regulator at a pre-determined voltage, wherein the band-pass shunt regulator comprises two transistors in series, the transistors connected across the micro-chip supply voltage and the micro-chip ground voltage.
 4. The method of claim 3, wherein one of the transistors comprises a p-type transistor and one transistor comprises an n-type transistor.
 5. The method of claim 3, further comprising connecting a plurality of de-coupling capacitances across the micro-chip supply voltage and the micro-chip ground voltage. 